.TH MPI_Win_create_keyval 3 "6/7/2023" " " "MPI"
.SH NAME
MPI_Win_create_keyval \-  Create an attribute keyval for MPI window objects 
.SH SYNOPSIS
.nf
.fi
.nf
int MPI_Win_create_keyval(MPI_Win_copy_attr_function *win_copy_attr_fn,
MPI_Win_delete_attr_function *win_delete_attr_fn,
int *win_keyval, void *extra_state)
.fi


.SH INPUT PARAMETERS
.PD 0
.TP
.B win_copy_attr_fn 
- copy callback function for win_keyval (function)
.PD 1
.PD 0
.TP
.B win_delete_attr_fn 
- delete callback function for win_keyval (function)
.PD 1
.PD 0
.TP
.B extra_state 
- extra state for callback function (None)
.PD 1

.SH OUTPUT PARAMETERS
.PD 0
.TP
.B win_keyval 
- key value for future access (integer)
.PD 1

.SH NOTES
Key values are global (available for any and all communicators).

Default copy and delete functions are available.  These are
.PD 0
.TP
.B MPI_WIN_NULL_COPY_FN   
- empty copy function
.PD 1
.PD 0
.TP
.B MPI_WIN_NULL_DELETE_FN 
- empty delete function
.PD 1
.PD 0
.TP
.B MPI_WIN_DUP_FN         
- simple dup function
.PD 1

There are subtle differences between C and Fortran that require that the
copy_fn be written in the same language from which 
.I MPI_Win_create_keyval
is called.
This should not be a problem for most users; only programmers using both
Fortran and C in the same program need to be sure that they follow this rule.


.SH RETURN VALUE FROM ATTRIBUTE CALLBACKS
The MPI-2 versions of the attribute callbacks should return either
.I MPI_SUCCESS
on success or a valid MPI error code or class on failure.
The MPI standard is ambiguous on this point, but as MPI-2 provides
the routines 
.I MPI_Add_error_class
and 
.I MPI_Add_error_code
that allow the
user to define and use MPI error codes and classes.

.SH THREAD AND INTERRUPT SAFETY

This routine is thread-safe.  This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks.  However, the routine is not interrupt safe.  Typically,
this is due to the use of memory allocation routines such as 
.I malloc
or other non-MPICH runtime routines that are themselves not interrupt-safe.

.SH NOTES FOR FORTRAN
All MPI routines in Fortran (except for 
.I MPI_WTIME
and 
.I MPI_WTICK
) have
an additional argument 
.I ierr
at the end of the argument list.  
.I ierr
is an integer and has the same meaning as the return value of the routine
in C.  In Fortran, MPI routines are subroutines, and are invoked with the
.I call
statement.

All MPI objects (e.g., 
.I MPI_Datatype
, 
.I MPI_Comm
) are of type 
.I INTEGER
in Fortran.

.SH ERRORS

All MPI routines (except 
.I MPI_Wtime
and 
.I MPI_Wtick
) return an error value;
C routines as the value of the function and Fortran routines in the last
argument.  Before the value is returned, the current MPI error handler is
called.  By default, this error handler aborts the MPI job.  The error handler
may be changed with 
.I MPI_Comm_set_errhandler
(for communicators),
.I MPI_File_set_errhandler
(for files), and 
.I MPI_Win_set_errhandler
(for
RMA windows).  The MPI-1 routine 
.I MPI_Errhandler_set
may be used but
its use is deprecated.  The predefined error handler
.I MPI_ERRORS_RETURN
may be used to cause error values to be returned.
Note that MPI does 
.B not
guarantee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.

.PD 0
.TP
.B MPI_SUCCESS 
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_ARG 
- Invalid argument.  Some argument is invalid and is not
identified by a specific error class (e.g., 
.I MPI_ERR_RANK
).
.PD 1
.PD 0
.TP
.B MPI_ERR_OTHER 
- Other error; use 
.I MPI_Error_string
to get more information
about this error code. 
.PD 1

